The present invention relates to nonwoven material (e.g., webs), and laminates including such nonwoven material, wherein the nonwoven material is, e.g., a particle-meltblown web coform structure having particulate material incorporated in the meltblown web (e.g., uniformly and homogeneously distributed therethrough).
Moreover, the present invention relates to methods of forming such nonwoven material, e.g., by particle-meltblown web coforming techniques, and methods of forming laminates including such nonwoven material, as well as uses for such nonwoven material and laminates.
It has been desired to provide porous particle-laden nonwoven material (such as webs), e.g., for filtering purposes, wherein the particles are loaded to a maximum amount in the web, the particles being held in the web without the web suffering from a "dusting" problem (that is, without the particles undesirably dropping out of the web). Moreover, it has been desired to provide such particle-laden webs as part of, e.g., a laminate, having various uses such as filtering uses.
U.S. Pat. No. 3,971,373 to Braun discloses a porous sheet product of a supported three-dimensional arrangement of particles, comprising a web of meltblown microfibers and the particles, no additional binder being necessary. This patent discloses that the particles are intermixed into a gaseous stream carrying the microfibers and become intermixed with the microfibers, the mixing occurring at a location spaced from the meltblowing die where the microfibers have become nontacky. The mixture is then collected on a collection screen, with the microfibers forming a web and the particles becoming dispersed in the web. The patent specifically discloses that the microfibers, mixed with the particles while the microfibers are not tacky, have no more than point contact with the particles, the particles usually being large enough to be physically entrapped within the interstices of the web. This patent further discloses that various polymers known to be useful in meltblowing, such as polypropylene, polyethylene, polyamides, and other polymers, can be used for forming the microfibers.
U.S. Pat. No. 4,433,024 to Eian discloses nonwoven sheet material laminates, including a permeable support fabric and, attached to the support fabric, a fibrous web including meltblown organic polymeric fibers and vapor-sorptive particles uniformly dispersed in the mass of fibers. This patent discloses that the support fabric can be either woven or nonwoven fabric, and can be laminated to both sides of the meltblown web to provide protection for the web and also to assure that particles are retained within the sheet material. This patent discloses that various means, such as adhesive bonding or attachment by sewing or ultrasonic welding, can be used to adhere the fabric to the sheet material. This patent also discloses that the particles can be mixed with the meltblown fibers under conditions that will produce an area contact with the particles, or, preferably, the particles are introduced into the stream of meltblown fibers at a point where the fibers have solidified sufficiently that the fibers will form only a point contact with the particles, as in the previously discussed U.S. Pat. No. 3,971,373.
U.S. Pat. No. 4,469,734 to Minto, et al. discloses formation of particle-laden web material, by incorporating absorbent particles into a stream of meltblown fibers while the fibers are still tacky, so that the particles are firmly attached to the fibers when the fibers set, a web being consolidated from the set fibers and particles. U.S. Pat. No. 2,988,469 to Watson discloses incorporation of particulate material in a stream of fibers while the fibers are still tacky (with no disclosure that the fibers are formed by meltblowing), the fibers being collected while still tacky, or afterwards, and formed into a web or sheet.
However, it is still desired to provide nonwoven meltblown webs having particles dispersed therethrough, wherein any problems with dusting are overcome, which webs can be formed easily using conventional meltblowing equipment.